1. Field of the Invention
The present invention relates to an antimicrobial article, more particularly, relates to fabrication of silicone composite with antimicrobial coating.
2. Description of the Related Art
Catheters and medical tubes are widely used to inject fluid and nutrients into arteries and veins, and to drain fluid or urine from urethra or internal organs. Nevertheless, catheter-associated infections are common, accounting for a large number of all nosocomial infections. Thus far, several types of catheters with antimicrobial effects have been developed, such as the silver-impregnated type, the TiO2-coated type, and the aminoglycoside type. Among metals with antimicrobial properties, silver has raised interest of many researchers due to its excellent antimicrobial properties and low toxicity.
The key challenges with developing these types of catheters are how to incorporate antimicrobial agent or coating onto the substrate and how to improve its antimicrobial effectiveness. One conventional method of incorporating antimicrobial agent into the silicone substrate is by blending via solution casting or melt compounding. The antimicrobial effectiveness of the conventional methods are limited by the relatively low amount of antimicrobial particles on the composite surface. The majorities of the antimicrobial agents are bound up within the polymer matrix, and therefore, are not easy to release to the composite surface. The use of additional antimicrobial agents with these methods may not improve the antimicrobial property of the material.
In order to overcome the existing drawbacks, a method of fabricating a double layer of silicone rubber tube was proposed by providing an internal layer in which an antimicrobial agent of zeolite carrying metallic silver is added to a transparent silicone rubber as a matrix, and an external layer made of transparent silicone rubber and formed so as to cover the internal layer, as described in Japanese Pat. No. 2000-88153. This method reduced the amount of antimicrobial agent and the cost of the product. However, a drawback of this method is the poor interfacial adhesion between the internal layer and the external layer (cover layer).
In recent years, there is increasing interest in altering the surface properties of the silicone substrate (catheter) in order to improve the efficiency of sterilization. A thin layer of antimicrobial agent (e.g. TiO2) coated onto the substrate surface by dipping the commercial catheter in an ethanol-water solution of a titanium dioxide sol and silicon oxide compounds, as described in J. Biomed. Mater. Res., Appl. Biomater., Vol. 58, pages 97-101 (2001), provides a good self-sterilizing and self-cleaning feature for the commercial catheter. An intermediate layer of modified silicone resin was taken to enhance the adhesion between TiO2 antimicrobial layer and the silicone substrate. However, this method is limited to preparation of antimicrobial silicone products with a very thin coating layer (less than about 1 μm in thickness). Once the coating thickness is close to 2 μm, the poor adhesion between antimicrobial particles and the onset of microcracks are not acceptable.
More recently, a composite consisting of TiO2 particle, the surface of which was modified with amino groups, and a silicone substrate through covalent bonding at their interface was developed, as described in J. Biomed. Mater. Res., Vol. 76A, pages 95-101 (2006). Although the obtained composite possesses good antimicrobial performance and strong bonding between TiO2 and the silicone substrate, the wide application of this method is limited by the complicated operating procedures and the relatively low amount of antimicrobial powders conglutinated in the substrate surface. Thus, the antimicrobial effectiveness is not satisfying.
In view of the above shortcomings, there exists a need for a simple, cost-effective method of coating antimicrobial agent on a substrate with excellent adhesiveness and antimicrobial effectiveness.